Post by SteveBy selecting 'factorial' and pressing alt-m, I see the origin of factorial.However, I do not see 'm' on the list of commands when I press right mousebutton. What does alt-m stand for?

This isn't actually a Smalltalk question but a general GUI one instead. There are two ways to invoke commands: you can press the right button on the mouse and then point to the option you want in the menu that pops up or you can use a keyboard shortcut to save time.

"pressing alt-m" means you hold one of the two keys labeled "ALT" on your keyboard and then you press "m".

If you use the right button to pop up a menu, you will see that many of the entries have an indication of what the corresponding shortcut is. So you can use the menus to see all possible commands and then the shortcuts to go faster the second time.

Post by Stevem was not on the list of commands, thus my question about it.

On this computer I don't have Pharo handy, but checked Squeak 3.10 and I see a "more..." option at the bottom of the right button menu for a text selection. By choosing that, I see a "implementors of it (m)" option.